Today there is no built in support in a service-oriented architecture (like web services) to inform a client of its state changes. This is an important feature for a service-oriented architecture as most computing systems are asynchronous in nature and the client needs to acquire such a change of the state through some asynchronous mechanisms.
In a service oriented component model (java services and/or web services), the state of a component is held by the service through its instance variables and/or session state variables and/or persistence storage media and/or using external resources. The service exposes its state information through various custom application programming interfaces (APIs). This interface model is not flexible and extensible, therefore each client has to program code to fit-in specific APIs and to understand the semantics as defined through the APIs. The clients are not flexible enough to query state data based on its exposed information model (data schema). The granularity and flexibility of these APIs vary with different implementation.
Therefore, what is needed is a framework to define mechanisms that enable a service to extend its state with change notification semantics a flexible service state exposure model through various queries on the state of the service using the exposed state information model (schema).